Yamaha MTN850-A 2017, Service Manual, Page: 258 / 560

VALVES AND VALVE SPRINGS
5-23
EAS30283
REMOVING THE VALVES
The following procedure applies to all of the
valves and related components.
TIP
Before removing the internal parts of the cylinder
head (e.g., valves, valve springs, valve seats),
make sure the valves properly seal.
1. Remove:
•
Valve lifter “1”
• Valve pad “2”
TIP
Make a note of the position of each valve lifter
and valve pad so that they can be reinstalled in
their original place.
2. Check:
• Valve sealing
Leakage at the valve seat

Check the valve
face, valve seat, and valve seat width.
Refer to “CHECKING THE VALVE SEATS”
on page 5-25.
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a. Pour a clean solvent “a” into the intake and
exhaust ports.
b. Check that the valves properly seal.
TIP
There should be no leakage at the valve seat “1”.
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3. Remove:
• Valve cotters
TIP
Remove the valve cotters by compressing the
valve spring with the valve spring compressor
“1” and the valve spring compressor attachment
“2”.
4. Remove:
•
Valve spring retainer “1”
• Valve spring “2”
•
Valve “3”
• Valve stem seal “4”
•
Valve spring seat “5”
TIP
Identify the position of each part very carefully so
that it can be reinstalled in its original place.
EAS30284
CHECKING THE VALVES AND VALVE
GUIDES
The following procedure applies to all of the
valves and valve guides.
1 2
Valve spring compressor
90890-04019
Valve spring compressor
YM-04019
Valve spring compressor attach-
ment
90890-04179
Valve spring compressor adapter
23 mm
YM-04179